Estrogen as an endocrine hormone is synthesized in vivo from cholesterol and is secreted from ovarian follicles and corpora lutea. When gonadotropins secreted from the anterior pituitary gland transmit signals to reproductive organs, follicle stimulating hormone (FSH) and luteinizing hormone (LH) regulating the menstrual cycle and enabling pregnancy are secreted and act on the ovaries, where estrogen and progesterone are secreted. Estrogen is a generic name for a group of hormones, including estradiol, estrone and estriol.
Ovaries in premenopausal women are main sources of estrogen. As women reach menopause, their aged ovaries are less likely to respond to hypophyseal gonadotropins (follicle stimulating hormone and luteinizing hormone), leading to a further shortening of the early follicular phase. As a result, the menstrual cycle and the ovulatory phase are more shortened, the production of progesterone is reduced, and the cycle is more irregular. Consequently, the ovarian follicles do not respond to hypophyseal gonadotropins, thus failing to produce estrogen any further. The reduced secretion of estrogen can have major effects on a woman's body, including the genitourinary system. Further, when ovulation stops, this leads to menopause, which signifies the end of menstruation, or the hormone reduction before menopause leads to the occurrence of menopausal symptoms.
The rapidly reduced estrogen in postmenopausal women results in increased dangers of psychological and emotional symptoms, for example, fatigue, excitement, sleeplessness, poor concentration, depression, memory loss, headache, anxiety and nervousness. Other possible dangers include fatigue and excitement resulting from sleep disturbance caused by recurrent facial flushing, intermittent dizziness, paresthesia, tachycardia, pyknocardia, nausea, constipation, diarrhea, arthralgia, myalgia, cold hands and feet, and weight gain. Further, postmenopausal women are very susceptible to osteoporosis and cardiovascular diseases, including heart diseases, hypertension and apoplexy, which are associated with an increase in mortality. Furthermore, changes in integumentary and genitourinary systems are caused, and the possibility of the incidence of autoimmune diseases, cataract and colorectal cancer is increased.
The most effective known method for treating menopausal symptoms, such as facial flushing, is to administer estrogen to women in need of estrogen supplementation.
However, long-term administration of synthetic estrogen may lead to cause serious problems such as the incidence of breast cancer and uterine cancer. Many recent reliable reports have asserted that long-term administration of synthetic estrogen as a hormone replacement therapy increases the possibility of inducing breast cancer. This issue remains highly controversial in all areas of society as well as in research groups. Although the exact cause for the incidence of breast cancer is not clearly demonstrated, the risk of the incidence of breast cancer in women having undergone synthetic estrogen replacement therapy is believed to be associated with estrogen exposure dose with time.
Under these circumstances, considerable research efforts have been directed toward finding phytoestrogen, a kind of vegetable estrogen, as a safer substitute for synthetic estrogen used in hormone replacement therapy. Phytoestrogen refers to a non-steroidal plant compound that exerts estrogenic effects in animals. Most cereals, fruits and vegetables known to have anticancer activity and are effective against heart diseases contain a slight amount of phytoestrogen.
Thus, there is an increasing demand for a safe drug or health functional food that is effective in treating women's menopausal symptoms without causing diseases such as breast cancer and uterine cancer.